Manufacture of materials of the nature of catalysts for the oxidation of oxidizable gases in admixture with air or oxygen



.Pateuted July' 14,1931 I I UNITED S A ES PATENT orsrcs 31m LAIBBB'L- or oxroan, nnenann, assm'noa' ro m. rnocassns mam-an, or LONDON, mrsmn, an ENGLISH Lima-an mum. comm,

muracrunn-or narnaransor'rnn naruns or caranvsrs ron rim oxrna'rron 01' mIZLBLE GASES IN ADMIZ'IUBE WITH AIR OB OXYGEN I I6 Drawing. Application illcd'nugult 83, 18538, Serial No. 301,696, and in Great Britain September 6, "1987.

This invention relates to improvements in themanufacture of materials of the nature of catalysts particularly materials suitable for employment in the oxidation of s in admixture with air or oxygen, an o ject of the invention being the production of solid materialspreferably in the form of hard granules havin a large' available surface and allowing the'ready passage of gases or vapours through them. Materials manufactured in accordance with this invention possess substantial advantages as oxidizing media for the oxidation of gases (such for instance as sulphur dioxide) passed'in ad- 1; mixture with suflicient air or oxygen over the said materials in a heatedv state in that they can beused at such temperatures that the oxidizing power bfithe materials can be continuously exerted over long periods of time. It is well known that chromium hydroxide (hydratedchromium oxide) will absorb oxygen when heated under pressure at a temperature of about 400 C.' butonly' a small proportion of the chromium which exists in 88 the trivalent state is thereby converted into hi her oxides of chromium in which the va ency is higher than three even if the heat- .ing be carried out in oxy on under a pressure as high as 12 (twelvg atmospheres. 80 It is also known that when hydrated chromium oxide is mixed with such basic oxides as Ag O, MgO, ZnO, CdO, and

PbO, and heated to 460 C. in oxygen at a pressure. of 12 (twelve) atmospheres, a considerable proportion of the trivalent chromium is converted into higher oxides of chromium. V,

,The present invention primarily consists in the production of hydrated chromium oxide such that when heated in air at the ordinary atmospheric ressure to a temperature of 350 C. to 400 it will absorbincreased quantities of oxygen and show an increased proportion'al conversion of trivalent chro- 4 mium into its higher oxides. This is achieved according to the present invention by recipitating chromium hydroxide in the orm of hydrogel and causin or permitting the .lat-

ter to adsorb an inso uble or slight y soluble base or bases. Materials so manufactured ossess great powers and advantages as cataysts or oxidizing media for the oxidation of oxidizable gases (such, for example, as sulphurdioxi e) when these gases are passed, 1n a re .with sufiicient air or oxygen 5 over them. If the temperature .of such materials be maintained at a suitable value, above 350 0., and sufiicient air or oxygen be used in the admixture, the materials are capablefof continuous use as oxidizing media over long so periods of time. a I We have found that when a cold aqueous 7 solution containing 10% by weight of a solu-, .ble chromium salt (such, for exam le, as chromium nitrate or chloride) is ad ed, in equivalent quantity, slowly, and with stirring, to a coldaqueous solution of caustic soda containing 1 part by weight of NaOH to each 2 parts by weight of water chromium hydrox'ide is eventually preclpitated in the form of a hydro l. Precipitation may not begin until some time has elapsed after the solutions have been mixed. The rooess may be carried out though not sore ily without stirring in which case the chromium hydroxide may appear in the form of a jelly. r v

If the precipitated'hydrogel of chromium hydroxide thus prepared is washedfree from soluble salts by distilled water. and then filtered and the product allowed to dry slowly so in air, at the ordinary temperature, the material undergoes marked shrinkage and, when the drying under these conditions is complete, a hard, brittle solid is obtained which shows a bright lustrous surface, after fracture, and which in thin layers is transparent. At this stage'of the drym it is important that the temperatureshould not be raised.

Further drying in 'acurrent of air at a higher temperature (say 1009 C.) causes the loss of more waterandthe product under-" goes further shrinkage and becomes harder. If, when thewater content has been reduced to about 10% the product be heated to a temperature of about 350 C. in a current of air, still more water isv removed although the material may still contain 4% to 5% of water as-. sociated with the chromium-oxide calculated asGr 'O This'water can 'onlybe removed by heating for long periods at much higher A temperatures. The material obtained after heating at a temperature of about 350 in air has, in a marked degree, the power of adsorbing considerable quantities of condensible gases and vapours. It contains a small proportion ofthe chromium in a higher state of oxidation than trivalent but it has no marked advantages as a catalyst or oxidizing medium.

When however, chromium hydroxide hydrogel is precipitated as described above and .Washed free from soluble salts, the wet hydrogel has, in a very marked degree, the power of adsorbing insoluble or slightly soluble bases when placed in contact with aqueous solutions of the salts of these bases.

. If, for example, the wet chromium hydroxide hydrogel be mixed with a dilute solution. of the acetate of calcium, or magnesium, or

.nickel, or cobalt, or manganese, or zinc and water does not remove these adsorbed bases. If now the chromium hydroxide hydrogel, containing an adsorbed base, or bases, be

washed, filtered and dried as described above,

the product may not be 'markedly different of from 350 to or slightly soluble bases and washing with ble salts and thereafter causing it to adsorb at least one slightl soluble base.

3. A process or the manufacture of catalytic material for the oxidation of oxidizable gases in the presence .of oxygen, comprising precipitating chromium hydroxide in the form of a hydrogel, mixing into said hydrogel a solution of a salt of at least one slightly soluble base so as to cause the said hydrogel to adsorb said base washing, filtering if necessary, and finally drying said hydrogel containing the adsorbed base or bases.

4. A process for the manufacture of catalytic material for the oxidation of oxidizable gases in the presence of oxygen comprising preparing a chromium hydroxide hydrogel, washing same free from soluble salts bringing the wet hydrogel into contact with an aqueous solution of a salt of at least one slightly soluble base to cause the hydrogel to adsorb said base, washing, filtering if necessary, and finally heating the hydrogel containing su'ch adsorbed base in a current of air and then drying (game at a. temperature BERTRAM LAMBERT.

in appearance from the simple dehydrated chromium oxide gel even if it contains as 'much as 20% of its weight of adsorbed base.

But if the material be heated for a sufficient time in a current of air at a temperature of about 350 to 400 C. the material discloses in addition to high absorptive properties great powers and advantages as a catalyst or oxidizing mediumffor the oxidation of oxidizable gases (such, for example,

as sulphur dioxide) when passed, in admixture with sufiicient air or oxygen, over the heatedmaterial even at atmospheric pressure.

When a mixture of sulphur dioxide and air is passed over these materials at a temperature of about 500 C.oxidation to sulphur trioxide occurs and progressively increases until a continuous high percentage conversion is obtained. v

The invention further includes the improved material prepared in the manner herein described.

What I claim is-:-

1. In the manufacture of catalytic materials, for the oxidation of oxidizable gases in the presence of oxygen, the step of causing a chromium hydrogel to adsorb at least one slightly soluble base.

2. A process for the manufacture of cata l ytic materials for the oxidation of oxidizable gases 1n the presence of oxygen, comprising preparing chromium hydroxide in the form of hydrogel, washing the same free from soluv csmrtcm or conmzcnou, Patent No.- 1,814,515. I I I .Granted July 14, 1931, to

I BERTRA'M LAMBERT? h Q it hereby certified that error appears inthe printed specification of the shove numbered potent requiring correction as follows: Page 2, line 58,.claim 1,

after the word .ehrominm" insert'the word hydroxidef same page, line 77, claim '3, strike out the words "or bases; and that the said Letters Patent should be resd'with thesecorre'ctions therein that the same may conform to the reeord of the ease in the Patent Offioe. Signed ahd sealed this 25thday of August, A. 1). l93l.;

M. J. Moore,

' (Sesl Acting Commissioner of Patents. 

